Alloy and method for the improvement of zinc base alloys



, 3,083,096 ALLOY AND METHOD FOR THE ROVEMENT F ZINC BASE ALLOYS Leslie J. Larrieu, San Marino, Calif., assignor to Morris P. Kirk & Son, Inc, Los Angeles, Calif., a corporation of California No Drawing. Filed Nov. 14, 1960, Ser. No. 68,674 8 Claims. ((31.75-178) Y The present invention relates generally to the nonferrous metal art, and particularly to a novel zinc base alloy and method of producing such alloy of improved mechanical properties from a zinc base alloy which has become contaminated during use as a die metal.

Zinc base alloys with the general composition 4% aluminum, 3% copper, .05 magnesium, 007% maximum lead, .005 maximum cadmium and .005 maxmium tin have been in constant use as sand cast metal forming dies for over 20 years (all composition values given herein are percent by weight based upon the final composition). During this usage, which usually consists of multiple melting and casting into new shapes, the alloy often becomes contaminated with lead, tin, cadmium and bismuth. Such contamination, depending upon the amount, can, and often does, render the alloy unsatisfactory for the intended service, such as for drop hammer forming dies, because of reduced mechanical strength of the alloy. A considerable economic loss is suffered by metal fabricators as a result of these conditions of impaired mechanical strength and undesirable physical properties of the used alloys, all of which is due to this alloy contamination. This loss is one of considerable magnitude for the aircraft and missile industries, which becomes evident when consideration is given to the very large tonnage now in use, most of which suffers from some degree of contamination.

Lead is the usual and most commonly encountered contaminant, followed in order by tin, cadmium and bismuth. Lead contamination is usually derived from the counter die, or punch, used with the zinc base alloy die in the stamping and forming of metal parts. Solders and low melting point alloys are fertile sources of lead, tin, cad- I I mium, and bismuth contaminants. However, lead is the principal contaminant and lead-antimony alloys are the chief source of contamination.

The users of such sand cast zinc base alloys experience a decrease in tensile strength from about 33,000 p.s.i. (pounds per square inch), for the uncontaminated alloy to about-23,000'p.s.i. for contaminated alloy containing approximately .10% 'lead. Similar-reductions in impact strength occur, such as from'about'12- ft. lbs; (footpounds) for the uncontaminated alloy to 1 or 2 ft. lbs. for the contaminated alloys containing approximately .10% lead.

Accompanying these severely reduced mechanical properties are such seriously affected physical properties as extremely coarse grain, unpredictable dimensional changes, accelerated growth and detrimental warpage. Hot cracking also is a serious condition which is discovered after the lead punch is cast on the inc alloy die.

These serious conditions usually are minimized by diluting the contaminants. Economically this is a very costly and unsound procedure. The aircraft and missile industries have practiced blending techniques wherein equal quantities of contaminated alloy and virgin alloy are melted together to yield a usable, castable alloy with properties intermediate-between those of the virgin alloy and the contaminated alloy.

It is an important object of this invention to provide 3,083,096 Patented Mai-.26, 1963 'ice 2 p a method for restoring substantial quantities of these contaminated alloy stocks to complete usefulness.

It is another object of this invention to provide a novel zinc base alloy having improved mechanical properties.

I have discovered that contaminated zinc base 'alloys, particularly those containing up to about .15 lead, can be restored to complete usefulness for sand cast forming dies by several operations including removing magnesium from the contaminated alloy to the extent that the magnesium content of the treated alloy preferably is less than about 03%. This generally is accomplished by melting the used, contaminated alloy and'treating the molten alloy with a halogenating reagent under conditions of time and temperature such that the magnesium halides'will escape from the molten alloy. A further improvement of the treated alloy is accomplished by introducing lithium therein in amounts of about .0005 to about .05 so that the treated alloy contains a residue of from about a trace to about .0005% lithium after treatment with nitrogen gas. An additional improvement is achieved by introducing beryllium into the alloy so that the treated alloy contains from about .0005% to about .01% beryllium. A still further upgrading in properties is attained by adjusting the copper content of the alloy so that theiinal alloy contains more than about 3% and not more than about 4.0% copper.

Additionally I have discovered that the addition of about .0005% to about .01% beryllium and about'.25% to about 1.0% copper to'used contaminated alloys, without prior magnesium reduction or removal, and without prior addition of lithium, imparts substantial improvement in mechanical properties, particularly tensile strength, to such alloys. The resulting alloy will contain from about 3.25 to about 4.0%, copper. Also markedly improved is the grain size of the alloy when sand cast. Furthermore, I have discovered that when beryllium is added alone, without prior or subsequent treatments or additions, a minimum addition of about 001% contributes to grain refinement and effectively reduces drossing characteristics of the alloy with consequent savings from dross loss. A greater such addition up to about 01% materially strengthens the alloy and increases the overall resistance of these alloysto intercrystalline oxidation. 1 have likewise discovered that these same metallurgical practices impart similar amounts of improvement to both used alloys containing low levels of contamination and virgin alloys when manufactured with new high purity metals.

The reasons for these operations will be readily understood from the following more detailed description of my invention, which is given primarily for purposes of illustration and not limitation.

The amount of aluminum in this class of alloy isusually limited to about 4%. If aluminum exceeds about 4.5%, some loss in ductility with consequent brittleness results. Aluminum forms with zinc an unstable phase designated beta phase. This beta phase is transformed below 200 F. into a'zinc-richalpha phase and an aluminum-rich gamma phase. The zinc-rich'alpha phase is susceptibleto oxidation and corrosion, which is accelerated by the presence of lead and other oxidi zable soft metals.

Copper increases ,the tensile strength of the 4% aluminum, balance zinc alloy and likewise increases impact strength when total amount is limited to about 3.5%. Copper forms'with zinc an eta phase, which is transformed to a great extent to an epsilon phase. These eta-epsilon phases-are'strengtheners to the alloy system Zn-Al-Cu, as wellas protectors to the corrodible alpha phase. The massive presence of eta-epsilon phases envelops the alpha phase and protects. it against intergranular oxidation,

which is lgnown to be caused and accelerated by the presence of the soft metals, lead, tin, cadmium and bismuth.

Magnesium is believed to be protective against intergranular corrosion to the Zn-Al and the ZnAl-Cu systems. Such protection to the coarser grain sized Zn-Al-Cu sand cast alloys is definitely questionable. This questionability is directly related to grain size. It has been definitely established in Patent No. 2,940,846, issued to me on June 14, 1960, that the presence of magnesium alfects impact strength and grain size of sand cast Zn-Al-Cu-Mg alloys. The efliect is one of diminishing impact strength and coarsening grain with increasing magnesium content.

The elfect of lead impurity upon the 4% Al, 3% Cu, .05 Mg, balance zinc alloy is amply illustrated by the fact that the addition of .06% Pb to this alloy reduces tensile strength from about 30,500 psi. to about 26,500 p.s.i., and reduces impact strength from about 12 ft. lbs. to about 3 ft. lbs.

The impurity elements, tin, cadmium, bismuth and antimony, either singly or in combination, exert similar detrimental efiects upon the mechanical properties of the 4% Al, 3% Cu, 05% Mg, balance zinc alloy. Combinations of lead and tin, and bismuth, lead and tin, also contribute to severe conditions of die cracking because of hot shortness. This hot shortness is due to the low melting points of the eutectics formed by the various impurity element combinations. i The impact strength, grain size and tensile strength of zinc base sand cast alloys of the composition 4% aluminum, 3% copper, both uncontaminated and contaminated with lead, are affected by the amount of magnesium present in the alloy. Theimpact strength for both uncontaminated and contaminated alloys is inversely proportional to the amount of magnesium present for the range, trace magnesium to .20% magnesium. Grain size and tensile strength are similarly afiected, although these effects are more pronounced with the contaminated alloys. The following test data amply illustrates the effects of magnesium upon tensile strength, impact strength and grain size of the 4% aluminum, 3% copper, .05-% lead, balance zinc-alloy in the unaged sand cast state.

TABLE 1 Percent Tensile Impact magnesium strength, strength, Grain size p.s.i. ft. lbs.

. 005 29, 778 9. 6 Medium fine. 022 30, 700 9. Medium. 040 29, 400 5. 8 Medium coarse. 063 27, 450 3. 5 Coarse. 078 27, 000 2. 0 D0.

Magnesium can be removed from these zinc base alloys with solid aluminum fluoride type fluxes at about 950 F., or preferably by gassing with C1 at about 900 F. Time and: temperature conditions employed are functions of magnesium removal whether by active gas or solid state AlF -KClNaCl fluxes. The lower the temperature, the

greater the required time. A preferred aluminum fluoride 4 role of lithium in metallic oxide reduction and sulfur removal:

Massive additions of lithium are removable from the alloy melt in a preferential manner with gaseous nitrogen as follows:

The alkali metal, preferably lithium, is added in ele mental form to the alloy, after magnesium removal, at about 900 F. After complete alloying and solution the melt is agitated mechanically for about 30 minutes, then completely skimmed of all dross. If heavy additions of lithium are required (01-05%), the excess of lithium is removed by gassing the melt with nitrogen at about 900 F. until removal of the excess lithium (to less than about .0005%) is accomplished as lithium nitride, in accordance with the above equation.

Beryllium in an amount less than about 01%, such as about .009%, or as low as .00l%, is added to the alloy melt in a copper-beryllium master alloy at about 950 F preferably after the lithium treatment. Beryllium fulfills the role of an anti-oxidant as it efiectiv ely prevents the absorption of oxygen into the alloy through preferential self-oxidation. It is a very effective grain refiner and phase strengthener, and adds to alloy fluidity and inhibits dross formation. Beryllium materially strengthens the eta-epsilon phase of the zinc-copper system which is by itself very effective in protecting the vulnerable alpha phase of the transformed beta phase from the zinc-aluminum system.

The final metallurgical operation involved in these restoration processes is the adjustment of the copper content of the alloy to a minimum level of about 3.25%. This adjustment preferably is made by the addition of pure copper in the form of wire or ingot. In many instances, particularly where total impurity content of the processed alloy approximates about .10%, I have found that the copper level better serves restoration purposes if the level is maintained at about 3.75% copper. In creased copper content contributes to increased mechani cal properties for both uncontaminated and contaminated alloys. Table 2, below illustrates the elfect of copper on the tensile strength of the 4% aluminum, balance zinc alloy.

This strengthening effect of copper is due to the increased amount of eta-epsilon phase of the zinc-copper system in the structure of the 4% aluminum, 30-40% copper, balance zinc alloy. In the case of the contaminated alloy, this eta-epsilon phase engulfs the transformed alpha phase of the zinc-aluminum system and protects it from the destructive intercrystalline oxidation processes which, when lead is present, become greatly accelerated.

In summary, it is apparent, therefore, that the application ofv the method of my invention to be used on contaminated zinc base alloys, preferably containing about 4% aluminum, about 3% copper, about .05 magnesium and variable amounts of impurities restores such alloys to usefulness as sand cast shapes for forming dies. These operations, as pointed out above, involve alloy alteration in the process of magnesium removal when required. The

magnesium removal accomplishes an improvement of impact strength, tensile strength and grain refinement. The lithium addition accomplishes deoxidation, desulfurization and conversion of metallic oxides dissolved in the alloy to metals. This adds to the promotion of soundness and improvement in mechanical and physical properties of the upgraded alloy. The beryllium addition enhances fluidity, grain refinement, phase strengthening and antioxidation protection in the restored alloy. Finally, the copper addition increases the proportion and total amount of eta-epsilon zinc-copper phase in the upgraded alloy. This serves to increase the mechanical properties of the finished alloy and protects it against destructive intercrystalline oxidation normally caused by the presence of soft metal contaminants such as lead, tin, cadmium, antimony and bismuth.

Table 3 below illustrates the comparative improvement attained by these operations and contains data showing relative tensile and impact improvement produced in a 4% aluminum, 3% copper, .045 magnesium, indicated percent lead, balance zinc alloy, sand cast by the designated treatments practiced in accordance with the method of the invention described hereinabove.

An example of the comparative improvements attained in a .116% lead, 4.1% aluminum, 3.1% copper, 045% magnesium 004% cadmium, 004% tin, balance zinc, alloy by the addition of beryllium alone, beryllium plus copper, and lithium plus beryllium plus copper, Without prior removal or percent reduction of magnesium, is illustrated in Table 4 below:

TABLE 4 Addition Addition Addition of of No or 005% Be .0005% Li, additions 005% Be and 005% Be,

.75% Cu and Tensile strength, p.s.i 25, 500 27,500 30,000 31, 900 Impact strength, ft. lbs. 2. 4 3. 6 3. 5 4.0 Brinell hardness 100 100 105 109 The following comparative mechanical test data, contained in Table 5 below, clearly illustrate the effect of these treatment when applied to a specification alloy with low level of contamination having the composition: 005% lead, 4.0% aluminum, 3.0% copper, 05% magnesium, balance zinc.

TABLE 5 Addition of Mg removed .0005% Li, to 015% and N0 005% Be, addition of treatment and 000.5% Li,

.50% Cu 005% Be,

and .50% Cu Tensile strength,.p.s.i 30, 275 34, 000 38. 500 Impact strength, ft. lbs 11.4 14.6 28.0 Brinell hardness 100 100 104 Table 6 below illustrates the comparative relative superiority of virgin alloys manufactured with the use of the lithium treatrnent and the addition of 005% beryl- 6 liufii, and the use of beryllium addition only as applied to a virgin alloy having the composition: 002% lead, 3.80% aluminum, 3.1% copper, 01% magnesium, balance zinc.

These data clearly illustrate that existing, uncontaminated alloys now in use can be considerably improved by the practices of lithium deoxidation and addition of beryllium for antioxidation, phase strengthening and grain refining. These data also show that new alloys of this class, and intended sand cast use, can be manufactured by using the metallurgical operations of my invention to produce highly improved and greatly superior zinc base alloys.

In summary it is clear that the application of the metallurgical operations of my invention can be practiced wholly, in part, or in combination, for the production of virgin alloys. It has also been amply demonstrated that the partial reduction, or almost complete removal of magnesium, is not in eithercase essential to the attainment of substantial improvement by the use of the remaining operations of my invention. It is quite evident from these data that the addition ofberyllium alone (from about 001% to about 009%) can be practiced for the improvement of both virgin alloys and the full range of contaminated alloys. The refinement of grain size, phase strengthening, improved alloy fluidity and lesseneddrossing characteristics during melting, render the beryllium addition very important and quite advantageous.

' The following detailed example illustrates the application of the method of my' invention to a specific situation:

EXAMPLE 1 After melt down, mixing and skimming of 34,520 lbs. of scrap reject dies, samples were taken for analysis and Mechanical properties (sand cast):

Tensile strength (p.s.i.) -1 25,250

Elongation (percent in 2") 2.0 Impact strength (ft. lbs.) 2.4 Br'inell hardness Grain size from fractured tensile bars Coarse Charpy method on A x A unnotched bars.

Magnesium Removal or Reduction Afterdeterr'nination of the general strength characteristics and impurity content of this lot of metal, the initial process treatment of magnesium removal was undertaken. On the basis of metallurgical experiences from several hundred previous operations, 1.6 lbs. of aluminum fluoride was added for each 1000 lbs. of alloy, or a total use of 55 lbs. of'this salt was made for the operation of magnesium reduction to a level not to exceed 03% Also used with the aluminum fluoride in the operation was approximately /2 lb. of NaCl-KCl mixture per 1000 lbs. of alloy under treatment, or approximately 16 lbs. of this salt mixture for the treatment of 34,000 lbs. of alloy.

This solid type fiux mixture was added to the alloy melt at 950 F., in about lb. portions, with the benefit of mechanical agitation. Each 10 lb. addition of flux mixture was allowed to completely react before additional quantities were added. Approximately 2 hours were consumed in conducting the operation, including final careful skimming of spent reacted material from the surface of the melt.

After verification of magnesium content by Quantometer analysis, the entire 34,000 lbs. were pumped to a clean coated pot. This transfer to a. clean kettle insured the complete separation of liquid metal from dross and fused, semi-liquid, spent flux. In its simplest form, although not empirical, this reaction can be represented as follows:

Many other methods of magnesium removal are available, including the use of chlorine gas (solid), ammonium; chloride (solid), zinc chloride (solid), zinc ammonium chloride, other solid halogen salts and other reactive gases.

Deoxidation Wit'h Lithium This transferred metal was then maintained at 950 F., while .0005% lithium was added in the form of .17 lb. of pure elemental lithium metal. After this addition of lithium, the resulting mixture was strongly agitated me chanically for about 45 minutes. Very thorough hand skimming of all dross and other non-metallic residues concluded this deoxidation, desulfurization and oxide reduction operation.

When excessive oxides, sulfur, or both are suspected in the metal, amounts or lithium greater than about .0005 are added. This excess lithium is removed pref erentially by gassing the molten metal with nitrogen at from about 900 to about 950 F. The reaction is symbolized by the following chemical equation:

The desirability of removing excess lithium is based upon the adverse effect of lithiumupo'n impact strength and an undesirable coloration imparted to sand cast ap r. ng-

Addition of Beryllium and Copper Percent Copper 57.8 Aluminum 39.75 Beryllium 2.41

This addition of. 83 lbs. of -pre-alloyed master alloy introduced .00S8% beryllium, .l35%, copper and .096% aluminum into the 34,000 lbs. of alloy undergoing treatment. These additions of inasteralloy and pure copper were made at about 925 F. with the aid of-mechanical agitation, Approximately 1 hour was requiredfor the complete solution of these additives. Final agitation and skimming concluded the process treatments. The finished alloy was cast by pumping it into 1000 lb. billets. The analysis of the processed alloy was as follows:

Percent Lead .055 Aluminum 3.80 Copper 3.60 Magnesium .02 Lithium .0001 Cadmium .0028 Tin .0032 Iron .005 Bismuth .0025 Beryllium .0058

Any discrepancy in the copper content of the resulting alloy is due to an unavoidable loss of copper during alloying. The lowered aluminum content of the alloy is due to losses sustained from the magnesium removal treatment. The resulting alloy, upon testing after sand casting, showed the following mechanical properties:

Tensile strength (p.s.i.) 33,775 Elongation (percent in 2") 2.0 Impact strength 1 (ft. lbs.) 9.2 Brinell hardness 100 Grain size from fractured tensile bars Fine (,harpy method on ,4" x unnotched bars.

It is apparent that a considerable amount of restoration of mechanical properties was achieved by applying the method of the invention to this particular alloy with its level of impurity contamination. Also of extreme importance was the grain refinement achieved by these treatments.

Additional examples of the results obtained by the use of the method of this invention in upgrading the mechanical properties of used and contaminated dies of zinc base alloys are summarized below:

EXAh-IPLE 2 Before After treatment treatment Composition (percent):

' 3. 70 3. 65 2. 3. 70 03 021 063 080 003 003 003 003 .001 .001 Beryllium None 006 Mechanical properties:

Tensile strength (p.s.i.) 26, 500 32, 750 Elongation (percent in 2" 2. 0 2. 0 Impact strength (ft. lbs.) 5. 0 8.1 Brluell hardness; 100 Grain size Coarse Fine EXAMPLE 3 Before Alter treatment treatment Composition (porcent):

Aluminum 3. 70 3. 75 Copper 3. 20 4. 00 Magnesium. 03 024 arl 060 .061 Cadmium .007. 007 Tin .009 .009 Bismuth .031 031 Beryllium None 006 Mechanical properties:

Tensile strength (p.s.i.) 23, 500 30, 600 Elongation (percent in 2") 1. 5 2. 0 Impact strength (ft. lbs.) 3. 8 8.0 Brlnnell hardness 100 100 Grain size Coarse Fine EXAMPLE 4 Before After treatment treatment Com osition percent):

A iumimnii 3. 80 3. 75 C pp g; Ma nesium T Pal l2 118 0028 0027 0024 0029 4 001 .001 Beryllium None 0057 Mechanical properties:

Tensile strength (p.s.i.) 25, 250 31, 000 Elongation (percent in 2") 2. 2.0 Impact strength (ft. lbs.) 6.0 7. 3 Brinell hardness. 100 100 Grain size Coarse Fine EXAMPLE Before After treatment treatment Corn osition percent):

A lnmim1r n Cooper .027 .01 Magnesium 142 13 0077 007 0117 011 031 030 Beryllium None 003 Mechanical properties:

Tensile strength (p.s.i.) 24, 400 28, 700 Elongation (percent in 2") 2.0 2.0 Impact strength (ft. lbs.) 3. 3 5. 3 Brinnell hardness 104 109 Grain size Coarse Fine Nora-All results obtained from sand cast specimens. Impact results obtained from K x bars.

Obviously many other modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that Within the scope of the appended claims the invention can be practised otherwise than as specifically described.

What is claimed is:

l. -A restored contaminated zinc base sand casting alloy having mechanical properties and refined grain size substantially similar to that possessed by a virgin zinc base alloy consisting essentially of, by weight, the following:

Aluminum, from about 3.5% to about 4.5%. Copper, from about 3.25% to about 4%. Magnesium, trace to about Lead, from about 0.14% to about .2%

Tin, trace to about .05%

Cadmium, trace to about .05%.

Bismuth, trace to about .05

Antimony, trace to .05%.

Beryllium, from about .0005 to about .0l%. Zinc, remainder.

2. A restored contaminated zinc base sand casting alloy having mechanical properties and refined grain size substantially similar to that possessed by a virgin zinc base alloy consisting essentially of, by weight, the following:

Aluminum, from about 3.5% to about 4.5%. Copper, from about 3.25% to about 4% Magnesium, trace to about .06%

Lead, from about 014% to about .2%.

Tin, trace to about .05%

Cadmium, trace to about .05

Bismuth, trace to about .05%

Antimony, trace to .05%

Beryllium, from about .0005 to about .01%. Zinc, remainder.-

1-0 3. A restored contaminated zinc base sand casting alloy having mechanical properties and refined grain size substantially similar to that possessed by a virgin zinc ba-se alloy consisting essentially of, by weight, the following:

Aluminum, from about 3.5 to about 4.5% Copper, from about 3.25% to about 4%. Magnesium, trace to about 03%.

Lead, from about 014% to about .2%.

Tin, trace to about .05

Cadmium, trace to about .05

Bismuth, trace to about .05%.

Antimony, trace to .05

Beryllium, from about .0005% to about .01% Zinc, remainder.

4. The method of restoring the mechanical and physical properties of a contaminated zinc base sand casting alloy consisting essentially of, by weight, about 4% aluminum, about 3% copper, about .05% magnesium, at

- least one of the soft metal contaminants selected from the group consisting of lead, tin, cadmium, bismuth and antimony present in an individual amount in excess of .007% and present in a collective amount of less than .25 and the remainder Zinc, which comprises melting the contaminated al-loy, adding a halide reactant to remove magnesium as a halide from the molten alloy to an amount less than 03%, thus restoring the properties of the contaminated alloy to substantially that of the virgin alloy.

5. The method of restoring the mechanical and physical properties of a contaminated zinc base sand casting alloy consisting essentially of, by weight, about 4% aluminum, about 3% copper, about .05% magnesium, at least one of the soft metal contaminants selected from the group consisting of lead, tin, cadmium, bismuth and antimony present in an individual amount in excess of 007% and present in a collective amount of less than 25% and the remainder zinc, which comprises melting the contaminated alloy, adding a halide reactant to remove magnesium as a halide from the molten alloy to an amount less than .03%, adding about .0005% to about .01% beryllium, thus restoring the properties of the contaminated alloy to substantially that of the virgin alloy.

6. The method of restoring the mechanical and physical properties of a contaminated zinc base sand casting alloy consisting essentially of, by weight, about 4% aluminum, about 3% copper, about .05% magnesium, at least one of the soft metal contaminants selected from the group consisting of lead, tin, cadmium, bismuth and antimony present in an individual amount in excess of 007% and present in a collective amount of less than 25% and the remainder Zinc, which comprises melting the contaminated alloy, adding a halide reactant to remove magnesium as a halide from the molten alloy to an amount less than .()3%, adding pure copper to increase the same to about 3.25% to about 4%, thus restoring the properties of the contaminated alloy to substantially that of the virgin alloy.

7. The method of restoring the mechanical and physical properties of a contaminated zinc base sand casting alloy consisting essentially of, by weight, about 4% aluminum, about 3% copper, about .05% magnesium, at least one of the soft metal contaminants selected from the group consisting of lead, tin, cadmium, bismuth and antimony present in an individual amount in excess of 007% and present in a collective amount of less than 25% and the remainder zinc, which comprises melting the contaminated alloy, adding a halide reactmt to remove magnesium as a halide from the molten alloy to an amount less than 03%, adding pure copper to increase the same to about 3.25% to about 4% and then adding about .0005% to about .0l% beryllium, thus restoring the 1 1 properties of the contaminated alloy to substantially that of the virgin alloy.

38. The method of restoring the mechanical and physical properties of a contaminated zinc base sand casting alloy consisting essentially of, by Weight, about 4% aluminum, about 3% copper, about 05% magnesium, at least one of the soft metal contaminants selected from the group consisting of lead, tin, cadmium, bismuth and antimony present in an individual amount in excess of .007% and present in a collective amount of less than .25 and the remainder zinc, which comprises melting the contaminated alloy, adding a halide reactant to remove magnesium as a halide from the molten alloy to an amount less than 103%, introducing from about .00025% to about .0005% of an alkali metal into the molten alloy to deoxidize the molten alloy, removing the alkali metal oxide as a dross, then removing any remaining alkali metal, adding pure copper to increase the same to about 3.25% to about 4% and then adding about .0005% to about .01% beryllium, thus restoring the properties of the contaminated alloy to substantially that of the virgin alloy.

References Cited in the file of this patent UNITED STATES PATENTS 1,596,761 Peirce et al Aug. 17, 1926 1,663,215 Peirce et a1. Mar. 20, 1928 1,883,235 Gonser Oct. 18, 1932 1,999,209 Queneau Apr. 3 0, 1935 2,412,045 Harrington Dec. 3, 1946 2,452,665 Krol-l et al Nov. 2, 1948 2,467,956 Bierman Apr. 19, 1949 2,940,846 lLarrieu June 14, 1960 FOREIGN PATENTS 375,244 Germany May 8, 1923 663,274 Germany Aug. 2, 1938 512,758 Great Britain printed 1939 638,733 Great Britain June 14, 1950 OTHER REFERENCES 

1. A RESTORED CONTAMINED ZINC BASE SAND CASTING ALLOY HAVING MECHANICAL PROPERTIES AND REFINED GRAIN SIZE SUBSTANTIALLY SIMILAR TO THAT PROCESSED BY A VIRGIN ZINC BASE ALLOY CONSISTING ESSENTIALLY OF, BY WEIGHT, THE FOLLOWING: ALUMINUM, FROM ABOUT 3.5% TO ABOUT 4.5%. COPPER, FROM ABOUT 3.25% TO ABOUT ABOUT 4%. MAGNESIUM, TRACE TO ABOUT 10%. LEAD, FROM ABOUT 0.14% TO ABOUT .2%. TIN, TRACE TO ABOUT .05%. CADMIUM, TRACT TO ABOUT .05%. BISMUTH, TRACT TO ABOUT 0.5%. ANTIMONY, TRACT TO .05%. BERYLLIUM, FROM ABOUT .0005% TO ABOUT .01%. XINC, REMAINDER.
 4. THE METHOD OF RESTORING THE MECHANICAL AND PHYSICAL PROPERTIES OF A CONTAMINATED ZINC BASE SAND CASTING ALLOY CONSISTING ESSENTIALLY OF, BY WEIGHT, ABOUT 4% ALUMINUM, ABOUT 3% COPPER, ABOUT .05% MANGNESIUM, AT LEAST ONE OF THE SOFT METAL CONTAMINANTS SELECTED FROM THE GROUP CONSISTING OF LEAD, TIN, CADMIUM, BISMUTH AND ANTIMONY PRESENT IN AN INDIVIDUAL AMOUNT IN EXCESS OF .007% AND PRESENT IN A COLLECTIVE AMOUNT OF LESS THAN .25% AND THE REMAINDER ZINC, WHICH COMPRISES MELTING THE CONTAMINATED ALLOY, ADDING A HALIDE REACTANT TO REMOVE MAGNESIUM AS A HALIDE FROM THE MOLDEN ALLOYS TO AN AMOUNT LESS THAN .03%, THUS RESTORING THE PROPERTIES OF THE CONTAMINATED ALLOY TO SUBSTANTIALLY THAT OF THE VIRGIN ALLOY. 